Tiling straight on timber or fix layer of ply?

[doug boardley]

I liken it to drink driving, you might not crash, or get caught everytime, but one day.............

 

[DHTiling]

Thats one way of putting it Doug...:lol:

 

[Grace'sDad]

I liken it to drink driving, you might not crash, or get caught everytime, but one day.............

And... no offence intended to the PVA "crew", but if you do this, like a drink-driver you're a blinkin' wally who should know better!

 

[honza1]

Well well

You say PVA has no place in tilling trade.

Why did I hear ever since that PVA should be used on walls and especialy ply when tilling?(to seal it)
When I was learning from old trades man he always said to seal walls or ply with PVA.
Even when I was working in refurbishment company.
Even friend tiler told me to use it.
And you hear it even in the shops often.

It seems to me that PVA nicely penetrates all dust on the surface of walls and make addhesive stick better rather than just tile staight on dusty wall.
I feel it is like plastering. Have you ever done plastering on dusty wall or existing old plaster without pva? It would just peal of (most likey).

And with ply I was told many times that it seals the top of the wood so it do not soak in water.

I was using PVA for years when in emploiment and never hear not to use it.
now selfemploied I do not know reason why I should not use it. Never heard about no problems with it.

PLEASE explain to me why is it so bad and what would you use?

I will be happy to learn som.. new

people just say I hope you did not use this and that but they never say why or what they would do. Dont make people ask just show what you got.

 

[doug boardley]

if I knew how to post the "pva vs primer" thread Honza I would, doubtless somebody will soon

 

[DHTiling]

The old saying again.. i have used it for years.....:mad2:....

Have read of this>>>>> http://www.tilersforums.com/tile-adhesive-grout-prep-forum/2511-p-v-versus-primers.html

dose PVA prevent ettringnite failure...i don't think so....and just coz an old school tiler or what ever has done it for years dose NOT say it is the correct method ...it just means they have used pva for years ...:smilewinkgrin:

 

[Grace'sDad]

It was sWe's post last year I think.
PVA not so much of a problem with acrylic addy but with cement based adhesives onto gypsum based walls, you will have chemical interactions between cement and gypsum - made worse by the PVA
Etringite crystals I seem to remember.....

I was called to a job in Lancaster - only 18 months old and the whole wall of tiles had de-bonded from the wall. Tiler's defense was "I PVA'd it properly".
Now it's gone legal.

 

[honza1]

well thanx for that I will check it out.

As another say- We are never to old to learn something new

and to all those past jobs hat are still there without prolems - Do not fix whats not broken.

But Thanx for advice.
Hope I did not ruin your bank holydays

 

[DHTiling]

Also this courtesy of Swe....

PVA stands for polyvinyl acetate, and it is a rubbery synthetic polymer. It is commonly emulsified in water and used as glue. Many know it simply as "wood glue", or "carpenter's glue".

Cementious materials, such as many tile adhesives and grouts, or other materials which contain cement, such as concrete, are alkaline. Simplified, that means they have a high pH.

Alkali slowly attacks polyvinyl acetate, forming acetic acid, which has a low pH. Cement doesn't dry per se; it cures through hydration, which means it binds the water you mix it with chemically. This causes the pH of the substance to rise dramatically. Introducing an acid negates that process to some extent, preventing the cement or conrete from binding all the water it needs to harden properly.

It is hydrolysis which gives cement and concrete products strength, and holds them together. Without this process, it would merely be the powder you started with.

The acetic acid which is formed when cement and PVA comes into contact, either through mixing them, or "priming" with PVA, will continually free the water bound in the cement, and that will weaken the bond and/or integrity of the material. The effect is accelerated if the material is subjected to moisture, which is more or less always the case.

PVA isn't water resistant. It becomes slightly live when exposed to moisture, and this in combination with the exposure to alkali, accelerates the forming of acetic acid. PVA which is marketed as "water resistant" or "exterior grade", has additives which makes them water resistant, but they're not alkali-resistant.

...

 

[honza1]

It was sWe's post last year I think.
PVA not so much of a problem with acrylic addy but with cement based adhesives onto gypsum based walls, you will have chemical interactions between cement and gypsum - made worse by the PVA
Etringite crystals I seem to remember.....

I was called to a job in Lancaster - only 18 months old and the whole wall of tiles had de-bonded from the wall. Tiler's defense was "I PVA'd it properly".
Now it's gone legal.

Thanx

I have came across similar in the past but never knew the real cause of it.
I have seen it on multyfinish plaster on top of send and cement.
I though that they probably did not use PVA.
BUT now I know.

 

[honza1]

I checked it out.

Will start using the primers now but as I read it - it seems really frightening.

THANX to all again.

 

[jay]

on the subject of olde sayings . you should never argue with someone sillier than yourself :8no challenge) just smile back